If there are panels on your Windsor roof, or you are thinking about them, there is an obvious hope: that the car will run on sunshine. Part of the year, with the car at home and a compatible setup, some of it can. The rest of the year, the roof makes too little to matter much to a car, and the charger does its work overnight. The useful thing is to know which months are which, and by how much. If you have not yet fitted a charger, our page on EV charger installation in Windsor covers the job in SL4, from Dedworth and Clewer to Old Windsor.
The figures below come from PVGIS, the European Commission’s solar calculator, for a 4 kWp array facing due south at 35° at Windsor. They are estimates for an unshaded roof, not a survey result or a promise of what any system will produce, and the per-day and charging-time figures are our arithmetic on them.
The year on one roof
PVGIS estimates about 4,002 kWh a year from that array, an average of about 11 kWh a day. The average hides a wide swing:
| Month | PVGIS output | Per day (our arithmetic) | Equivalent hours at 7 kW (our arithmetic) |
|---|---|---|---|
| January | about 161 kWh | about 5.2 kWh | about 45 minutes |
| June | about 482 kWh | about 16.1 kWh | about 2.3 hours |
| July | about 486 kWh | about 15.7 kWh | about 2.2 hours |
| December | about 140 kWh | about 4.5 kWh | about 40 minutes |
December’s output is about 29% of June’s. A 7 kW charger puts roughly 7 kWh into the car for each hour it runs, so the last column is what a whole day’s generation would equal if every kilowatt-hour went into the car and the house used none of it. In practice the house always uses some.
What a Windsor summer can add
In June and July, a sunny day on that roof makes roughly 16 kWh. The fridge, the router and whatever else is running take their share as it is generated, and with a compatible setup the surplus that would otherwise be exported can be diverted into the car. How much is left depends on what your household is doing in the middle of the day, which your own bills and the survey tell you better than any average.
Two things decide whether a Windsor household sees the benefit:
- The car has to be at home in daylight. A car that leaves at eight and returns at six misses most of the useful hours on weekdays. Weekends, days working from home and a second car that stays on the drive are where summer solar charging happens.
- The charge does not have to be large. A car that is topped up little and often from the roof through the summer needs less from the grid overnight.
What winter charging looks like
In December the same roof makes about 4.5 kWh on an average day, the equivalent of roughly 40 minutes at 7 kW (our arithmetic), and the house needs most of it. Solar charging is not a winter plan in Windsor. The winter plan is the overnight off-peak window.
That is where the smart rules help. Every new home chargepoint sold in Great Britain has had to be smart since 30 June 2022, so the charger can be scheduled into your tariff’s cheapest hours, and a compatible setup can prioritise sunny hours when there is surplus to use. The same charger handles both seasons; only the schedule changes.
The months in between
March to May and August to October sit between the two extremes. The pattern is gradual: from spring the roof begins to leave a surplus on good days, and by autumn it shrinks again. Rather than set rules by the calendar, the simplest approach is to leave the overnight schedule in place all year and let solar diversion add what it can on days the car is home.
Before you plan around the roof
Windsor’s housing matters here. Across the SL4 postcode district, about 33% of 13,517 EPC-certificated homes are flats. In a flat the roof belongs to the building, so panels, and any solar link to a charger, start with the freeholder. In a Dedworth or Old Windsor semi with its own roof and drive, the two are much easier to design together.
The Royal Borough says a chargepoint on a drive is generally exempt from planning permission, provided the site is not a listed building or scheduled monument, a wall-mounted outlet is no more than 0.2 cubic metres and a separate upstand no more than 1.6 metres high. In the town centre, where an Article 4 Direction applies, check with the council before fitting anything on a visible wall. Our page on solar panels in Windsor covers the roof side.
The network and the paperwork
Windsor’s town centre is in SSEN Distribution’s Southern Electric Power Distribution area, so a chargepoint in SL4 is notified to SSEN by your installer, as are panels. A 7.4 kW charger draws 32 A continuously, and most homes have a 60 A, 80 A or 100 A main fuse, so load management usually avoids an upgrade.
Grants, kit and the borough’s numbers
DVLA records 5,973 privately kept plug-in vehicles across Windsor and Maidenhead at the end of June 2026, up from 4,651 a year earlier, about 28% more (our arithmetic). We quote the private figure because most plug-ins registered in the borough are company vehicles counted at a registered address. Owners of houses get no grant towards a charger; renters and people who own and live in flats can get 75% of the cost, up to £500 per socket, with private off-street or allocated parking. The claim must be made through an OZEV-authorised installer; tell us your situation at the quote stage, and see who qualifies for the chargepoint grant. For the charger we fit, the EnSmart SmartBee-M, see our guide to home EV charger installation.
Sources: European Commission JRC, PVGIS 5.3 (4 kWp, 35°, due south, 14% losses, building-mounted, PVGIS-SARAH3 2005 to 2023), run 15 October 2026; Royal Borough of Windsor and Maidenhead, Installing an EV chargepoint at home and Permitted development rights; EPC Advisor, SL4 (government EPC register data); NESO GB DNO licence areas (May 2024) and SSEN Distribution, Who we are; Electric Vehicles (Smart Charge Points) Regulations 2021; DfT and DVLA, VEH0142 licensed plug-in vehicles by local authority, private keepers, 2026 Q2 and 2025 Q2 (published 23 September 2026); GOV.UK, Changes to electric vehicle chargepoint grant schemes from 1 April 2026 (updated 7 July 2026). Per-day figures, ratios and charging times are our arithmetic.